Preperation for new lawn

Hi, i wonder if someone can advice me. i have just installed a herringbone drainage system in my lawn because the drainage was so poor. The lawn is 46m2. I have used 25m of pipes and 4 tonne of pea gravel, leading into a 3ft soakaway. What I am unsure about is if I should be doing anything else prior to laying new turf. One supplier suggested i add 7 1/2 tonne of topsoil, but will this help improve the drainage or is that just to have a top quality lawn? (It will be well abused by three kids!)Someone else suggested I lay the turf on a bed of sand but is that just to help make the ground level or will it contibute to good drainage? I don't want to lay new turf on the existing soil only to find that the rainwater can't get through the heavy soil into the drainage that i have installed! I'm just confused as to what i should add, and in what quantities, so I would be grateful if someone could offer me some advice. Thanks :confused:

 

Hi Renfrew - I'd steer clear of the sand if I were you. First of all it doesn't hold any nutrients, so the roots from your new turf would be likely to stay in the inch or so of rootzone material that it was grown on. Sand can also be a problem unless you get the particle sizes analysed to make sure it's compatible with your native soil.

You also have to make sure that the pea gravel doesn't get contaminated with different sized particles (of sand or soil), because this could "cap it off", and reduce the drainage capacity. With golf greens and high quality turf surfaces, a layer of 2 inches or so of intermediate material is often used, called a blinding layer - this is perfectly matched particles that prevents any contamination of the drainage system. In your case, maybe you could look at a membrane or something to keep the gravel clean?

7 1/2 tonnes of topsoil would raise your lawn by about 5 inches when firmed (sorry, too early for exact calculation ), so you need to be sure that you're happy for your lawn to be raised by that much - plus an extra inch when you have the turf on top.

On the positive side, it will help retain nutrients and moisture, and as long as it's good soil, it would help the drainage a little bit. Remember that you only want to prevent excess moisture - having all of it running straight into your drainage system would be counter productive in the summer, so extra soil will help retain a useful amount of moisture.

If you do decide to go for more soil, try to get the smae material that the turf was grown on - some of thelarger suppliers can supply this. It's more expensive, but it will help the rooting of the new turf, and if the turf growers are using it, you know it's good stuff

 

I agree that you shouldn't lay a layer of sand but do support the addition of large amounts of sharp or grit sand to heavy soil types. I insist however that it should be incorporated by rotovator. Because of differing expansion and contraction rates of stone and soil it will cause fractures and air pockets both in summer and winter. I am impressed with the drainage system you have installed but the water must be able to reach it so some sort of rootzone should be created. Only adde the topsoil if it is of rootzone qulaity